To provide a pulper having an improved ability of disaggregation treatment compared to a conventional pulper even if the pulper has the nearly same size of the equipment as that of the conventional one, and further to prevent a light-weight foreign matter from plugging the lower part of an impeller to improve the operability.

A second strainer 1 is attached to a tub 12 of the pulper A, and a disaggregated product is collected by a second chamber 2. A light-weight foreign matter N is caught by a collecting part 5 of a groove with a bottom to reduce the plugging of the light-weight foreign matter N to the lower part of an impeller 7.